[Blood levels of hormones regulating calcium-phosphorus metabolism in men exposed to a 120-day period of hypokinesia].

Nine healthy male volunteers were exposed to head-down tilt (-4.5 degrees) for 120 days. The concentrations of parathormone, calcitonin, gastrin, growth hormone, total and ionized calcium were measured in plasma. Prolonged exposure to antiorthostatic hypokinesia led to significant changes in the hormonal regulation of calcium-phosphorus metabolism, the most important of which was an enhanced secretion of the parathyroid hormone. The increased concentration of calcitonin and gastrin was a secondary response to the higher content of ionized calcium. The phase-like changes in the somatotrophic hormone secretion were induced by variations in the parathormone concentration in blood, on the one hand, and by a reduction of plastic processes, on the other.